The present invention relates to a plasma display panel (hereinafter often referred to as "PDP") which is a plate display of a self-activation luminescence type using gas discharge, and more particularly to PDP with a color filter provided on a front plate.
In general, PDP comprises two opposed glass substrates, a pair of electrodes systematically arranged in the glass substrates, and a gas (mainly Ne or the like) sealed therebetween. A voltage is applied across the electrodes to produce discharge within minute cells around the electrodes to emit light from each cell, thereby displaying information. Systematically arranged cells are selectively subjected to discharge luminescence in order to display information. Such PDPs are classified into two types, a direct current type PDP, wherein electrodes are exposed to a discharge space (DC type), and an alternating current type (AC type) wherein electrodes are covered with an insulating layer. Each of these types is further classified into a refresh drive system and a memory drive system according to display functions and memory drive systems.
FIG. 1 is an embodiment of the construction of an AC type PDP. In the drawing, the front plate and the back plate are shown separately from each other. As shown in the drawing, two glass substrates 1, 2 are arranged parallel and opposite to each other. Both the substrates are disposed so as to be held while leaving a given space therebetween with the aid of barrier ribs 3 provided, parallel to each other, on the glass substrate 2 as a back plate. Composite electrodes each comprising a transparent electrode 4 and a bus electrode 5 as a metallic electrode are provided parallel to each other on the back side of the glass substrate 1 as the front plate, and a dielectric layer 6 is provided so as to cover the composite electrode. Further, a protective layer 7 (MgO layer) is provided on the surface of the dielectric layer 6. On the other hand, address electrodes 8 are provided between the barrier ribs 3 on the front side of the glass substrate 2 as the back plate so that the address electrodes 8 are parallel to each other and orthogonal to the composite electrodes. Further, a phosphor 9 is provided so as to cover the wall surface of the barrier ribs 3 and the bottom face of cells.
The AC type PDP is of a plane discharge type and constructed so that an alternating voltage is applied across the composite electrodes on the front plate and an electric field leaked in the space produces discharge. In this case, since alternating voltage is applied, the direction of the electric field changes according to the frequency. Ultraviolet light produced by the discharge permits the phosphor 9 to emit light, and light passed through the front plate is viewed by an observer.
Regarding such color PDP, the present inventor has proposed various modifications. However, at the present time, color PDP having satisfactorily good contrast could have not been developed due to unsatisfactory brightness of the PDP per se.
For example, according to the present inventor's finding, reducing the reflectance to improve the contrast is effective in improving the visibility of an image on the display, and methods which are considered effective for realizing this include:
(a) a method wherein ND (neutral density) filter properties are imparted to the front plate; PA1 (b) a method wherein Nd.sub.2 O.sub.3 is placed in the front plate to exhibit an absorption property in a region other than a primary region of the spectrum of the phosphor; PA1 (c) a method wherein the place other than the phosphor layer is filled with a low-reflectance material, that is, a method wherein a black matrix is formed; PA1 (d) a pigment is incorporated into the phosphor layer; PA1 (e) a pigment layer is formed in front of the phosphor layer; PA1 (f) a color filter is provided which, corresponding to cells for red, green, and blue, is permeable to only a single wavelength of a luminescence spectrum.
Since, however, PDP, unlike CRT, has no sufficient margin for the brightness, the formation of a black matrix (method (c)) and the formation of a color filter (method (f) are considered effective for increasing the contrast while minimizing the reduction of the brightness. For color PDP, in order to provide a satisfactory angle of visibility, it is necessary to provide the black matrix and the color filter on the inside of the front plate. For this purpose, however, the color filter should withstand a temperature of about 450 to 600.degree. C. or a higher temperature and emit no gas in the course of the substrate production process. In this respect, the color filter, for a liquid crystal display device, in current use as such cannot be used in the above-described modified methods.
(i) The formation in advance of a color filter using a color glass paste or a glass paste with an inorganic pigment dispersed therein on a glass substrate as a front plate by printing for the formation of a thick film, or (ii) the formation in advance of a color filter by photolithography using the above paste, to which photosensitivity has been imparted, followed by the formation of a composite electrode, a dielectric layer, and a protective layer thereon is considered as a method for overcoming this problem associated with the provision of a color filter of three colors, red, green, and blue in PDP having the above construction.
In the above PDP, for structural reasons, the pattern of the color filter provided on the front plate should be parallel to the pattern of the phosphor of the opposed back plate, meaning that the pattern of the composite electrode (transparent and bus electrodes) of the front plate and the pattern of the color filter intersect each other at 90.degree.. Further, since the thickness of the color filter is 2 to 10 .mu.m, when the color filter is formed directly on the glass substrate, the electrode should be laid across a difference in level (2-10 .mu.m) between the pattern portion and the non-pattern portion of the color filter.
In the above composite electrode, the formation of the transparent electrode by vacuum deposition or by sputtering is preferred from the viewpoint of forming a good thin film. However, when the transparent thin film electrode is formed on the color filter, the formation thereof across the difference in level of 2 to 10 .mu.m without creating breaking is very difficult. Further, in the formation of the bus electrode on the difference in level, the presence of the difference in level poses a further problem that the thickness, line width, and shape of the edge of the electrode are affected by the difference in level, resulting in unstable operation.